1. Field of the Invention
The present invention is related to a method for detecting an amount of cloth in a drum washing machine, and more particularly, to a method for detecting an amount of cloth in a drum washing machine, in which a change in revolutions per minute of a motor(RPM) is measured for a preset duration in a disentangle step in a spinning cycle for detecting an amount of cloth.
2. Discussion of the Related Art
As shown in FIG. 1, a background art washing machine has a driving circuit, provided with a motor 3 adapted to be driven by a driving power fed externally for transmission of a rotating power to a drum, a speed sensing unit 4 for sensing a rotating speed of the motor 3, a computing/controlling unit 1 for receiving a signal detected in the speed sensing unit 4, selection signals from a key pad(not shown) and sensed signals generated in different sensors(not shown) and providing lot of signals, and a motor driving unit 2 for rotating the motor 3 either in a regular or reverse direction in response to a control signal from the computing/controlling unit 1.
Washing cycle and spinning cycle of the drum washing machine conducted by the foregoing driving circuit will be explained.
In the washing cycle, the computing/controlling unit 1 receives the rotating speed of the motor 3 through the speed sensing unit 4, selection signals from the key pad, and sensed signals of different sensors and provides lots of control signals according to the received signals. The control signals from the computing/controlling unit 1 switches the motor driving unit 2 so that a regular direction current is applied to the motor 3 to rotate the motor 3, a rotation force of which motor 3 is transmitted to a pulsator (not shown) through a clutch, to rotate the pulsator. As a result of pulsator rotation, a mechanical friction is occurred between the laundry in the drum and the pulsator. The computing/controlling unit 1 keeps on controlling the motor 3 for a preset time period such that the motor 3 is rotated in a regular direction at a preset RPM. Then, after a preset time period, the motor 3 is turned off for a preset time period again for decelerating and stopping the motor 3. Next, when the motor 3 comes to a stop, the computing/controlling unit 1 provides a control signal for switching the motor driving unit 2 to apply a reverse direction current to the motor 3. Then, the motor 3 is rotated in a reverse direction, selectively transmitting a rotation force to the pulsator through the clutch, to rotate the pulsator. As a result of pulsator rotation, a mechanical friction is occurred between the laundry in the drum and the pulsator. The computing/controlling unit 1 keeps on controlling the motor 3 for a preset time period such that the motor 3 is rotated in a reverse direction at a preset RPM. Then, after a preset time period, the motor 3 is turned off again for decelerating and stopping the motor 3. This regular or reverse direction rotation control of the motor 3 by the computing/controlling unit 1 is conducted repeatedly until an entire washing is completed. That is, as the regular and reverse direction rotations are repeated, a strong mechanical friction occurs between the pulsator and the laundry.
In the meantime, as shown in a flow chart in FIG. 3, the spinning cycle of the washing machine has an error determining step S11.about.S13 for comparing a number PC of times of attempts for detecting a cloth amount and a preset reference number to determine either entry into a spring cycle or an occurrence of an unbalance error, a laundry disentangling step S21 and S22 for, when the entry into the spinning cycle is determined in the error determining step S11.about.S13, for rotating the drum in a reverse direction at a speed in conducting a laundry disentangling cycle, and, after a preset time period, measuring a RPM change to detect cloth amount in the drum, an eccentricity determining step S31 and S32 for rotating the drum in a regular direction at a speed to measure an eccentricity based on the RPM change and compare a preset reference eccentricity and measured eccentricity to determine an eccentricity pass, a laundry re-disentangling step S41 for selectively conducting the error determining step S11.about.S13 or the eccentricity determining step S31 and S32 according to a result of the eccentricity determining step S31 and S32, and a main spinning step S51 for selectively spinning the drum at a specific RPM according to a result of the eccentricity determining step S31 and S32 to extract water from the laundry in the drum.
When the spinning cycle is started, a number PC of times of cloth amount detecting attempts is counted and stored in the computing/controlling unit 1. The computing/controlling unit 1 then compares a preset reference number of times (for example, 40 times) to the number PC of times of the cloth amount detecting attempts counted, and, if a laundry disentangling step is going on more than the reference number, a laundry unbalance state in the drum is determined to display an unbalance error on a display unit (not shown) and control various peripheral devices to stop all the operation of the washing machine S11.about.S13. In this instance, if the computing/controlling unit 1 determines the number PC of times of cloth amount detecting attempts is below a reference number of times, the motor 3 is controlled through the motor driving unit 2 to carry out the laundry disentangling cycle S21 in which the drum is rotated in a reverse direction at a preset RPM. At the same time, a RPM change is measured after a preset time period from the time when the drum is rotated at a constant RPM in the laundry disentangling step S22.
That is, as shown in FIGS. 2 and 4, a RPM change is measured to detect a cloth amount at a time point "A" after elapse of a preset time period from the laundry disentangling step by rotating the drum in a reverse direction at "II" RPM (for example, 50 RPM). If a Hall sensor generates ten pulses in one rotation of the motor 3 and a number of the pulses are stored at every one second, the RPM at every one second can be obtained. If 100 pulses are sensed for a first one second and 150 pulses are sensed for the next one second, the first 10 revolution per a second equals 600 RPM and the next 15 revolution per a second equals 900 RPM. For example, if a time period of the drum rotation per one pulse is 100 msec, we can obtain 10.sup.2 .times.10.sup.-3 .times.60=600 RPM. And, even though the computing/controlling unit 1 controls the drum to be at "II" RPM, the drum may rotate at a RPM deviated from the "II" RPM depending on the cloth amount. That is, in the "II" RPM when the laundry rotates independent of the drum with a position change of the laundry as the drum rotates, a fall of the laundry from "III" in FIG. 4 to a bottom of the drum causes a speed difference. When the laundry falls from "III" to the bottom, the RPM change is great if the cloth amount in the drum is little and the RPM change is little if the cloth amount in the drum is great because falling of the laundry is continuous. As an example, as shown in FIG. 4, if laundry presents only at "a" in the drum, it will take much time for the laundry to reach to "III" again after the laundry falls down from the "III" to the bottom, and a drum speed when the laundry moves toward "III" and a drum speed when the laundry falls from "III" will be different. However, laundries present at "a", "b" and "c" respectively, as laundries at "b" and "c" keep moving toward "III" after a laundry falls down from "III", there is not a great speed change. Accordingly, a cloth amount in a drum can be detected utilizing a principle of a RPM change according to the cloth amount.
Next, at "B" in FIG. 2, the computing/controlling unit 1 raises RPM of the motor 3 to "I" RPM for determining proceeding to the spinning cycle, which is a RPM when the laundry rotates together with the drum. In this instance, an eccentricity is measured based on a RPM change sensed by the speed sensing unit 4 at "C" while the motor 3 is under constant speed control (S31). Then, the measured eccentricity and a preset reference eccentricity are compared to determine an eccentricity pass (S32). If a result of the eccentricity comparison turns out that proceeding into a main spinning is not allowable, the number PC of times of cloth amount detecting attempts is increased by unity and compared to the preset reference number (40 time, for example), to carry out the disentangling cycle again according to a result of the comparison. If the result of the eccentricity comparison turns out that proceeding into a main spinning is allowable, the drum is rotated in a specific RPM, to carry out a main spinning in which the laundries in the washing tub are extracted of water (S51).
In the meantime, it is required to set an adequate time period from the laundry disentangling step to the time point "A", being a cloth amount detecting time point, in the cloth amount measuring step (S22), if not, an occurrence of error in the cloth amount detection is highly probable. That is, since a span of time between a time point at which the process proceeds into the laundry disentangling step and "A" time point is a time period before the RPM change enters into a converging process, with a great change of RPM, it is highly liable that the cloth amount is determined to be little even if the cloth amount is great due to the great RPM change. Accordingly, the background art method for detecting a cloth amount in a drum washing machine has problems in that much time is required until operation of the washing machine is stabilized and unnecessary laundry disentangling steps are carried out due to occurrence of an eccentricity error in the eccentricity determining step, because, in the background art method, the cloth amount is detected when the RPM is stabilized after application of a certain phase angle to the motor.